Results from NASA's LCROSS mission, which crashed into a crater on the south pole of the moon, were released today. There is water!

This isn't particularly surprising, for those who have been following events, but here is a little bit of history and background, and why this is actually pretty exciting:

Why we don't expect waterFirst of all, the moon is pretty small. It's big for a moon, especially compared to Earth, but in terms of being able to hold onto an atmosphere, there's just not enough mass. Being able to hold onto volatiles (gases, light molecules) depends on two things: how strong the gravity is, the temperature. Temperature matters because the hotter the gas is, the faster its molecules are moving, and the easier it is for them to reach escape velocity. The moon hasn't got the mass to hold onto things like water, given its location in the solar system (closer to sun = hotter.) Since there is no atmosphere, water would remain gaseous (instead of being able to freeze out or be liquid - you need pressure for that, for water at our distance from the sun - and the gas would escape because it's too hot & not enough gravity.

So, no water on the moon. However, the Apollo missions did bring back rocks that had trace water in them. The problem was, it was a real possibility that those rocks had been contaminated by water from Earth.

Why we might expect waterWater on the moon could in theory be created in situ (right there). If you have rocks hanging around on the moon (which it has plenty of), and those rocks contain oxygen - not the gas, but minerals that have oxygen in them - then it's possible that as the solar wind (protons, or hydrogen) smacks into those rocks it could knock the oxygen off. Then, with oxygen floating around (briefly) and hydrogen from the solar wind, you are likely to form a water molecule.

Ok, so now you have a water molecule. You still have the problem that it's too hot and there isn't enough gravity for the moon to hold onto it. The thing is, though, that the water won't just immediately fly away. Instead, it may wander around near the moon's surface, waiting for just the right energy kick to get it going. Just because the average gas molecule (and more than just that) are going too fast to hold on, doesn't mean that all molecules are going too fast. Some of them will be slower, and will stay for a brief while until they get knocked faster by a solar wind particle or something. So there should be small (trace) amounts of water around on the moon, in the top part of the soil, before they wind up wandering into space. This is what India's mission Chandrayaan-1 found, confirming other less-clear mission findings.

This doesn't help with persistent water though. If we want to use water for a manned mission, we really need more than what Chandrayaan-1 found. Let's go back to our water molecule wandering around near the moon's surface.

Every now and then, a water molecule will find its way to the polar regions, and land in a crater. What's special about these craters? The main thing is that near the pole, they are in perpetual night. Since they don't get any sunlight, they remain very, very cold (-238C, or -396.4F). Once our water lands in one of these craters, then, it will actually freeze despite the lack of atmosphere. In this way, we can slowly over time build up a reservoir of frozen water.

LCROSS MissionBasically this mission involved crashing a probe into the moon, which then kicked up a big dust plume. An orbiting spacecraft then measured the water content of the dust kicked up. The answer is: Yes, there is water!

"Multiple lines of evidence show water was present inboth the high angle vapor plume and the ejecta curtain created by theLCROSS Centaur impact. The concentration and distribution of waterand other substances requires further analysis, but it is safe to say[the crater] holds water."

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That's great. It's almost like cutting down a tree to count the rings, just less damaging.

If a tree is sufficiently large, it seems like you can just bore a little hole to the center and get an idea of the strata that way. You wouldn't strip away much phloem, and can fill the part with material if there's any worries about structural integrity. I don't know what they actually do, but that seems like a more apt simile. (The moon is like a very very large tree. )

Yay! Water on the moon! I heard from a random guy in a coffee shop today. I'll drink to that!

Well Sonic, I'm glad you set me right there. As you can tell, I know as much about the exploration and understanding of the solar system is I do botany. It's great learning new stuff, especially metaphors!

If you're dinkum about doing your best for the environment, kill yourself and feed the worms.

Xinzang wrote:India discovered water on the moon before the U.S. mission, but NASA is trying to take credit as usual.

I don't think NASA is actively trying to take credit and discredit India's mission; I think people just didn't hear about the India mission before and unfortunately most news articles are rolling with it (though the first article I read on the results mentioned the Chandrayaan mission). India's mission discovered trace amounts of water, the point of LCROSS was to figure out if there could be a lot more water hidden in those craters. And there was!

Xinzang: 1) I mentioned Chandrayaan-1 in this article, 2) if you want to be nitpicky, Chandrayaan-1's certainly wasn't the first discovery of water on the moon (although it was the most clear-cut), and 3) NASA actually built the instrument on Chandrayaan-1 that did the detecting.

NASA in no way has downplayed the significance of India's mission. If you're not reading it in the news, that's bad news reporting, not NASA's fault. It was certainly mentioned in NASA's press release. India's contribution to science certainly was very substantial.

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